In this study, the effect of poly (lactic acid)-oligomer (OLLA) on cold flow properties, IC engine performance and subsequently, exhaust gas emission characteristics is evaluated using microwave synthesized biodiesel from soybean oil. Biodiesel was synthesized by achieving maximum 99% conversion using KOH as catalyst at 60 degrees C under optimum reaction time of five minutes. Cloud point, pour point, flash point and fire point of synthesized biodiesel were analyzed as reference properties. OLLA is synthesized in absence of catalyst at 150 degrees C with the targeted molecular weight M-n similar to 1000 Da and density similar to 1.21 gm/cm(3). Subsequently, by blending ethyl lactate stabilized OLLA with biodiesel,"the cloud point, pour point, flash point and fire point were reduced significantly. Polarizing optical microscopic images during temperature scan relate the effect of OLLA on cloud point crystal morphology which delayed the crystal formation with reduction in crystal nucleation density and size of the crystals. Rheological analyses are conducted to understand the Newtonian flow regime at lower temperature and change in the viscosity and flow activation energy of biodiesel in the presence of neat as well as with ethyl lactate stabilized OLLA. The engine performance test reveals the comparative utilization of brake specific fuel consumption and break thermal efficiency with significant reduction in carbon monoxide and incombustible hydrocarbon in the exhaust gases. Hence, present research demonstrates the use of OLLA for improvement in the cold flow properties of biodiesel and the exhaust gas emission characteristics. (C) 2015 Elsevier Ltd. All rights reserved.